Ingenol-3-angelate is a diterpene ester that can be isolated from various Euphorbia species. The compound is currently used in the treatment of actinic keratosis. Angelic esters are prone to isomerization of the double bond to form the tiglate esters. Furthermore, ingenol-3-angelate is also prone to rearrangement to afford ingenol-5-angelate and ingenol-20-angelate.
WO2012/083953 discloses the synthesis of ingenol 3-(3,5-diethylisoxazole-4-carboxylate), a molecule devoid of the stability problems occurring to ingenol 3-angelate. The molecule is presently subject of clinical development for the treatment of actinic keratosis. The characteristics of the solid form of ingenol 3-(3,5-diethylisoxazole-4-carboxylate) have not been reported. The discovery of new forms of pharmaceutically useful compounds provides an opportunity to improve their performance.